Before the 49ers hosted the Seahawks in December at Candlestick Park, safety Donte Whitner was asked why the script could be flipped after Seattle had handily won the previous two matchups.

"First and foremost, we're at home," Whitner said. "We understand that it's a different ballgame when we're up there in their arena. We understand that when they come here, it's a lot more difficult for them. They don't have the crowd noise behind them to mess with our offense."

Whitner was right. The outcome was different. But six weeks after the 49ers' 19-17 win on Dec. 8, they'll have to prove they can do it at CenturyLink Field, the site of the two most lopsided losses of the Jim Harbaugh era, in the NFC Championship Game on Sunday.

As anyone remotely interested in the much-anticipated meeting knows, the 49ers (14-4) have lost by a combined score of - say it all together now - 71-16 in their previous two visits to Seattle, where the Seahawks (14-3) have won 16 of their past 17 games, 10 by at least 10 points.

On Sept. 15, the 49ers lost 29-3 as quarterback Colin Kaepernick had a career-high three interceptions and a career-worst passer rating (20.1). The humiliating conclusion starred Seahawks cornerback and chief 49ers antagonist Richard Sherman, who celebrated a fourth-quarter interception by dancing with the SeaGals and playfully patted Harbaugh, his former college coach, on the rear after the final whistle.

Sherman then tsk-tsked those who predicted a 49ers win by referencing Seattle's 42-13 romp in December 2012.

"They might not have watched the last game that we played them," Sherman said. "I don't know what the score was. You guys know?"

Four months after Sherman's sarcastic query, 49ers defensive tackle Justin Smith was posed a question similar to the one fielded by Whitner in December. What's going to prevent another shellacking in Seattle?

"I just think we're playing better football," Smith said. "Defensively, we've done pretty well against them. The last time we went up there, we kind of lost it in the fourth quarter, but we're not too worried about that. We know what we have to do."

It's not pie-in-the-sky chatter. The 49ers, who trailed 5-0 at halftime in Week 2, do have legitimate reasons to believe they can overcome the NFC West champions and their raucous fans.

For starters, they won't be missing an integral ingredient. In the 2012 blowout in Seattle, Smith was sidelined with a torn triceps tendon and running back Marshawn Lynch headlined a rushing attack that collected 176 yards, the most allowed by the 49ers in two years.

In Week 2, the 49ers didn't have wide receiver Michael Crabtree, leaving Anquan Boldin as their only available wideout with more than 38 career catches. Kyle Williams, who was released in November, was the No. 2 wide receiver, which allowed Sherman to shadow - and silence - Boldin (one catch, 7 yards).

In December, Boldin and Crabtree combined for 10 catches and 133 yards as the 49ers' had some success against Seattle's lesser cornerback, Byron Maxwell. A 2011 sixth-round pick, Maxwell had an interception, but allowed five catches for 61 yards.

In the postseason, Boldin and Crabtree have taken turns posting 100-yard games, and tight end Vernon Davis has a touchdown in each contest.

"It's tough on defenses when you have two guys outside capable of having big games, and then you have Vernon inside matched up with linebackers," Boldin said. "So it gives defenses fits."

The victory over Seattle in December was part of a season-ending run that suggested the 49ers are this season's hot-at-the-right-time team. They have arrived in Seattle on an eight-game winning streak during which they've taken to the road to beat red-hot Arizona, overcome Green Bay quarterback Aaron Rodgers in freezing conditions and clinically dispatched the Panthers, who had won 11 of their previous 12 games.

It's folly to attempt to attach much significance to Harbaugh's ever-fluctuating moods with the media, but he was particularly jocular Friday. Harbaugh happily fielded a question about a racehorse named after him and was pleased to hear the 3-year-old colt was an underdog in a race Saturday. Harbaugh has often said he finds being underestimated to be a competitive advantage and the 49ers will enter CenturyLink Field as 3 1/2-point underdogs with a tortured recent history in Seattle.

49ers at Seahawks

Spotlight on: ILBs NaVorro Bowman and Patrick Willis. They can play a big role in limiting the Seahawks' two biggest offensive weapons: between-the-tackles RB Marshawn Lynch and fleet-footed QB Russell Wilson. In the 49ers' 19-17 win in December, Bowman sent a first-quarter message by whacking a scrambling Wilson, collecting a sack and forcing a fumble that rolled out of bounds. Such plays have left an imprint on Wilson, who said of Willis and Bowman last week: "I don't think they can get any faster. They can chase me down like that." The NFL's top tacklers in the postseason: Bowman (21) and Willis (19).

They limit Lynch: Lynch has produced four of the top six rushing performances against the 49ers in the Jim Harbaugh era. In the past two games in Seattle, he's had 209 rushing yards and five total TDs.

They keep Wilson in the pocket: The Seahawks ranked 26th in passing yards per game, but were tied for 10th - with the 49ers and four other teams - in completions of 40-plus yards (10). Big plays result when Wilson extends plays and the secondary breaks down.

They commit fewer than two turnovers: They have committed seven turnovers in their past two trips to Seattle, including five in Week 2. Since 2011, they are 31-5-1 when they have fewer than two giveaways (5-6 when they don't).

THE SEAHAWKS WILL WIN IF ...

They don't let Gore get going: In the 49ers' past two wins against the Seahawks, Frank Gore has averaged 120.5 rushing yards. In their past two losses to the Seahawks, he's averaged 22 yards and 2.9 yards a carry.

The officials aren't flag-happy: Seattle's secondary employs an in-your-face style that straddles the line between inspired and illegal. The Seahawks were flagged for three defensive-holding penalties (one declined) in their December loss to the 49ers.

The 12th Man rattles the visitors: The Seahawks are an excellent team, but the environment is a big reason the worst two losses of the Harbaugh era have been in Seattle.